CHAPTER 1

INTRODUCTON

1.1 OVERVIEW:

The Project Entitled “POWER TRANSFORMER PROTECTION

USING MICROCONTROLLER-BASED RELAY” designed with Peripheral

Interface Controller (PIC 16F877A). Utility companies have enormous amounts of

money invested in transformers of all types, including distribution and power

transformer. Operating, maintaining, and inspecting all power transformers are not

an easy work. In order to reduce burden on maintenance of such transformers a new

idea has been discovered.

This project is mainly used to protect the transformer from getting worn

out due to electrical disturbances. The electrical parameters like current, voltage of

the transformers are fed as base values, using a keypad to the Peripheral Interface

Controller and the output signal is provided to operate a relay by comparing the

base values with the operating electrical parameters. The application consists of a

board of electronic components inclusive of a PIC 16F877A microcontroller with

programmable logic. It has been designed to work with high accuracy. The

electrical parameters of the power transformer such as voltage and current are fed to

the Peripheral Interface Controller as base values. The voltage and current value

during the operation of the power transformer is monitored and fed to the controller.

These values are monitored using a LCD display. By comparing these values the

Peripheral Interface Controller produces a trip signal which operates the relay and

in turn the connectivity between main supply and the power transformer is cut off,

1

thus protecting the power transformer from malfunctioning.

1.2 ORGANIZATION OF THE THESIS:

This paper mainly deals with the protection of power transformer

from various faults. The second chapter deals with the various methods already

existing in the protection of the transformer from various faults. The various faults

occurring in the transformer and the steps taken to protect the device from these

faults are also discussed. The components of the project and the embedded system

are explained in the same chapter. The next chapter gives an elaborate description

of the PIC microcontroller and its working. This chapter mentions the core features

and peripheral features of the PIC16F877A. The various memory organizations and

the ports description are detailed in this chapter. The fourth chapter contains the

idea of the software used in the project and the variation code. The fifth chapter

describes the hardware implemented in the project and the working principle of the

various components of the hardware. The choice of relay considering the various

factors is also listed out in this chapter.

2

CHAPTER 2

PROTECTION SYSTEM OF TRANSFORMER

2.1 INTRODUCTION:

The protection system of transformer is inevitable due to the voltage

fluctuation, frequent insulation failure, earth fault, over current etc. Thus the

following automatic protection systems are incorporated.

1. Buchholz devices:

A Buchholz relay, also called a gas relay or a sudden pressure relay, is

a safety device mounted on some oil-filled power transformers and

reactors, equipped with an external overhead oil reservoir called a

conservator. The Buchholz Relay is used as a protective device sensitive

to the effects of dielectric failure inside the equipment. It also provides

protection against all kind of slowly developed faults such as insulation

failure of winding, core heating and fall of oil level.

2. Earth fault relays:

An earth fault usually involves a partial breakdown of winding

insulation to earth. The resulting leakage current is considerably less than

the short circuit current. The earth fault may continue for a long time and

creates damage before it ultimately develops into a short circuit and

removed from the system. Usually provides protection against earth fault

only.

3

3. Over current relays:

An over current relay, also called as overload relay have high current

setting and are arranged to operate against faults between phases. Usually

provides protection against phase -to-phase faults and overloading faults.

4. Differential system:

Differential system, also called as circulating-current system provides

protection against short-circuits between turns of a winding and between

windings that correspond to phase-to-phase or three phase type short-

circuits ie, it provides protection against earth and phase faults.

The complete protection of transformer usually requires the

combination of these systems. Most of the transformers are usually

connected to the supply system through series fuses instead of circuit

breakers. In existing method the transformer does not have automatic

protective relays for protecting the transformer.

4

2.2 TRANSFORMER – DEFINITION

A device used to transfer electric energy from one circuit to another,

especially a pair of multiple wound, inductively coupled wire coils that affect such a

transfer with a change in voltage, current, phase, or other electric characteristic.

Fig 2.1 Basic Transformer

5

2.3 THE UNIVERSAL EMF EQUATION

If the flux in the core is sinusoidal, the relationship for either winding

between its number of turns, voltage, magnetic flux density and core cross-sectional

area is given by the universal emf equation (from Faraday’s Law):

…(2.1)

E is the sinusoidal rms or root mean square voltage of the winding,

f is the frequency in hertz,

N is the number of turns of wire on the winding,

a is the cross-sectional area of the core in square meters

B is the peak magnetic flux density in Tesla

P is the power in volt amperes or watts,

2.4 NECESSITY FOR PROTECTION

Transformers are static devices, totally enclosed and generally oil immersed.

Therefore, chances of faults occurring on them are very rare. However, the

consequences of even a rare fault may be very serious unless the transformer is

quickly disconnected from the system. This necessitates providing adequate

automatic protection for transformers against possible faults.

6

2.5 COMMON TRANSFORMER FAULTS

As compared with generators, in which many abnormal conditions may arise,

power transformers may suffer only from:

1. Open circuits

2. Overheating

3. Winding short-circuits

2.5.1 Open circuit Faults:

An open circuit in one phase of a 3-phase transformer may cause undesirable

heating. In practice, relay protection is not provided against open circuits because

this condition is relatively harmless. On the occurrence of such a fault, the

transformer can be disconnected manually from the system.

2.5.2 Overheating Faults:

Overheating of the transformer is usually caused by sustained overloads or

short circuits and very occasionally by the failure of the cooling system. The relay

protection is also not provided against this contingency and thermal accessories are

generally used to sound an alarm or control the banks of fans.

2.5.3 Winding Short-circuit Faults:

Winding short-circuits (also called internal faults) on the transformer arise

from deterioration of winding insulation due to overheating or mechanical injury.

When an internal fault occurs, the transformer must be disconnected quickly from

the system because a prolonged arc in the transformer may cause oil fire. Therefore,

relay protection is absolutely necessary for internal faults.

7

2.6 PROPOSED METHOD

In proposed method, monitoring and protecting the power transformer from

overvoltage and over current are performed automatically by using PIC

microcontroller.

2.6.1 Components of the project:

The protection of power transformers that we have implemented as our project

exclusively contains the following as shown in the Fig. 2.2

Rectifier, filter and Regulating circuit (Power circuits)

Voltage measuring circuit using Potential Transformer

Current measuring circuit using Current Transformer

Keypad and LCD display

Driver circuit and a Relay

PIC 16F877A microcontroller board

8

Fig 2.2 Block Diagram of Protection of power transformer using

Microcontroller based relay

2.7 OVERVIEW OF EMBEDDED SYSTEM

An Embedded system is any computer system hidden inside a product other

than a computer.

You will encounter a number of difficulties when you writer embedded-

system software in addition to those you encounter when you write

applications.

Response— Your system may to react to events quickly.

Testability— Setting up equipment to teat embedded software can be

difficult.

9

Debugability— Without a screen or a keyboard, finding out what the

software is doing wrong is a troublesome problem.

Reliability—Embedded systems must be able to handle any situation without

human intervention.

Memory Space—Memory is limited on embedded systems, and you must

make the software and the data fit into whatever memory exists.

Program installation—You will need special tools to get your software into

embedded systems.

Power Consumption—Portable systems must run on battery power, and the

software in these systems must conserve power.

Processor Hogs—Computing that requires larger amounts of CPU time can

complicate the response problem.

Cost—Reducing the cost of the hardware is a concern in many embedded

system projects; software often operates on hardware that is barely adequate

for the job.

Embedded systems have a microprocessor and a memory. Some have a serial

port or network connection. They usually do not have keyboards, screens, or

disk drives.

2.7.1 Components of an Embedded System

A computer is a system that has the following or more components.

A microprocessor

A large memory comprising the following two kinds:

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a. Primary memory (semiconductor memories-RAM, ROM and fast

accessible caches.)

b. Secondary memory (magnetic memory located in hard disks,

diskettes and cartridge tapes and optical memory in CD-ROM)

Input units like keyword, mouse, digitizer, scanner etc.

Output units like video monitor, printer etc.

Networking units like Ethernet card, front-end processor-based drivers, etc.

I/O units like a modem, fax cum modem, etc.

An embedded system is one that has computer-hardware with software

embedded in it as one of its most important component. It is a dedicated computer-

based system for an application(s) or product. It may be either an independent

system or a part of a larger system. As its software usually embeds in ROM (Read

Only Memory) it does not need secondary memories as in a computer.

An embedded system has three main components

It has hardware. Figure2.3 shows the units in the hardware of an embedded

system.

It has main application software. The application software may perform

concurrently the series of tasks or multiple tasks.

It has a real time operating system that supervises the application software

and provides a mechanism to let the processor run a process as per

scheduling and do the context-switch between the various processes. RTOS

defines the way the system works. It organizes access to a resource in

sequence of the series of tasks of the system. It schedules their working and

execution by following a plan to control the latencies and to meet the

11

deadlines. Latency refers to the waiting period between running the codes of

a task and the instance at which the need for the task arises.

It sets the rules during the execution of the application software. A small-

scale embedded system may not need an RTOS. An embedded system has

software designed to keep in view three constraints:

i. Available system memory

ii. Available processor speed and

iii. The need to limit power dissipation when running the system

continuously in cycles of wait for events, run, stop and wake-

up.

2.7.2 Programming the PIC in C:

Compilers produce hex file that is downloaded into ROM of the

microcontroller. The size of the hex file produced by the compiler is one of the

main factors to be considered while programming the microcontroller, because the

microcontroller have limited on chip ROM.

The assembly language produces hex file that is much smaller than C

programming, on the other hand programming 8051 in C is less time consuming

and much easier to write, but size of hex file produced is much larger than if we use

assembly language which may lead to increase in memory size for even a small

application so it decreases the application speed. Although, the following are some

of the major reasons for writing C programs instead of assembly.

1. It is easier and less time consuming to write than assembly.

2. C is easier to modify and update.

3. C code is portable to other microcontrollers with little modifications.

12

2.8 EMBEDDED SYSTEM AND DEVELOPMENT TOOLS

Embedded software development is typically done on a host machine,

different from the larger machine on which the software will eventually be

shipped to customers.

A tool chain for developing embedded software typically contains a cross-

compiler, a cross-assembler, a linker/locator, and a method for loading the

software into the target machine.

A cross-compiler understands the same C language as a native compiler

(with a few exceptions) but its output uses the instruction set of the target

microprocessor.

A cross-compiler understands as assembly language that is specific to your

target microprocessor and outputs instructions for that microprocessor.

A linker/locator combines separately compiled and assembled modules into

an executable image. In addition it places code, data, startup code, constant

strings, and so on at suitable addresses in ROM and RAM.

Linker/locators produce output in a variety of formats; it is up to you to

ensure that your liker/locator’s output is compatible with the tools you use

for the loading software into your target.

13

2.9 MICROCONTROLLER FOR EMBEDDED SYSTEMS

In the literature discussing microprocessors, we often see the term embedded

system. Microprocessor and Microcontroller are widely used in embedded system

products. An embedded product uses a microprocessor (or microcontroller) to do

one task and one task only. A printer is an example of embedded system since the

processor inside it performs only one task; namely, getting the data and printing it.

Fig 2.3 Block Diagram for Microcontroller unit

14

CHAPTER 3

PIC MICROCONTROLLER

3.1. INTRODUCTION TO MICROCONTROLLER:

Microcontroller differs from microprocessor in many ways. First of all, the most important difference is its functionality. In order to operate a microprocessor, other components such as memory or components for receiving and sending data must be added to it externally. In short, microprocessor is the heart of the computer.

On the other hand, microcontroller is designed to be all of that in one. No

other external components are needed for its application because all the necessary

peripherals are already built into it. Thus we save time and space needed to

construct devices.

What is PIC and why you go for PIC?

PIC stands for Peripheral Interface Controller as coined by microchip

technology

PIC is very popular microcontroller world wide

Microchip is the first manufacturer of 8 pin RISC MCU

Focus on high performance cost effective field programmable embedded

control solution

3.1.1 Need for Microcontroller:

Microcontroller is a general-purpose device which has in-built CPU memory

and peripherals to make it act as a mini-computer

15

Microcontroller has one or two operational codes for moving data from

external to CPU

Microcontroller has many bit handling instructions

Microcontroller works faster than microprocessor because of rapid

movement of bits within the chip

Microcontroller can function as a computer with the addition of no external

parts

3.2. CORE FEATURES:

High-performance RISC CPU

Only 35 single word instructions to learn

Operating speed: DC – 20 MHz clock input

DC – 200 ns instruction cycle

Up to 8K x 14 words of Flash Program Memory,

Up to 368 x 8 bytes of Data Memory (RAM)

Up to 256 x 8 bytes of EEPROM data memory

Interrupt capability (up to 14 internal/external

Eight level deep hardware stack

Direct, indirect, and relative addressing modes

Power-on Reset (POR)

Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)

Watchdog Timer (WDT) with its own on-chip RC Oscillator for reliable

operation

Programmable code-protection

Power saving SLEEP mode

16

Selectable oscillator options

In-Circuit Serial Programming (ICSP) via two pins

Only single 5V source needed for programming capability

In-Circuit Debugging via two pins

Wide operating voltage range: 2.5V to 5.5V

High Sink/Source Current: 25 Ma

Commercial and Industrial temperature ranges

Low-power consumption:

< 2 Ma typical @ 5V, 4 MHz

20Ma typical @ 3V, 32 kHz

< 1Ma typical standby current

3.3. PERIPHERAL FATURES:

Timer0: 8-bit timer/counter with 8-bit prescaler

Timer1: 16-bit timer/counter with prescaler

Timer2: 8-bit timer/counter with 8-bit period register, prescaler and

postscaler

Two Capture, Compare, PWM modules

Capture is 16-bit, max resolution is 12.5 ns.

Compare is 16-bit, max resolution is 200 ns.

PWM max resolution is 10-bit.

10-bit multi-channel Analog-to-Digital converter

Synchronous Serial Port (SSP) with SPI. (Master Mode) and I2C.

(Master/Slave)

USART/SCI with 9-bit address detection.

17

Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS controls

3.4. ARCHITECTURE OF PIC 16F877A

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Fig 3.1 Architecture of 16F877A

The complete architecture of PIC 16F877A is shown in the fig 3.1 that

gives details about the specifications of PIC 16F877A. Fig 2.2 shows the

complete pin diagram of the IC PIC 16F877A.

3.5 TABLE SPECIFICATIONS

3.6 PIN DIAGRAM OF PIC 16F877

Fig. 3.2 Pin diagram of PIC16F877A

DEVICE PROGRAM FLASHDATA

MEMORY

DATA

EEPROM

PIC

16F877A8K 368 Bytes 256 Bytes

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3.7 PIN DESCRIPTION:

Pin Name DIP

Pin#

PLCC

Pin#

QFP

Pin#

I/O/P

Type

Buffer

Type

Description

OSC1/CLKIN 13 14 30 I ST/

CMOS(4)

Oscillator crystal input/external clock source input.

OSC2/

CLKOUT

14 15 31 O -

Oscillator crystal output. Connects to crystal or resonator in crystal oscillator mode. In RC mode, OSC2 pin outputs CLKOUT which has 1/4 the frequency of OSC1, and denotes the instruction cycle rate

MCLR/VPP/

THV

1 2 18 I/P ST

Master clear (reset) input or programming voltage input or high voltage test mode control. This pin is an active low reset to the device.

RA0/AN0

RA1/AN1

2

3

3

4

19

20

I/O

I/O

TTL

TTL

PORTA is a bi-directional I/O port.

RA0 can also be analog input0

RA1 can also be analog

20

RA2/AN2/

VREF-

RA3/AN3/

VREF+

RA4/T0CKI

RA5/SS/AN4

4

5

6

7

5

6

7

8

21

22

23

24

I/O

I/O

I/O

I/O

TTL

TTL

ST

TTL

input1

RA2 can also be analog input2 or negative analog reference voltage

RA3 can also be analog input3 or positive analog reference voltage

RA4 can also be the clock input to the Timer0 timer/counter. Output is open drain type.

RA5 can also be analog input4 or the slave select for the synchronous serial port.

RB0/INT

RB1

RB2

RB3/PGM

33

34

35

36

36

37

38

39

8

9

10

11

I/O

I/O

I/O

I/O

TTL/ST(1)

TTL

TTL

TTL

PORTB is a bi-directional I/O port. PORTB can be software programmed for internal weak pull-up on all inputs

RB0 can also be the external interrupt pin.

RB3 can also be the low voltage programming input

21

RB4

RB5

RB6/PGC

RB7/PGD

37

38

39

40

41

42

43

44

14

15

16

17

I/O

I/O

I/O

I/O

TTL

TTL

TTL/ST(2)

TTL/ST(2)

Interrupt on change pin.

Interrupt on change pin

Interrupt on change pin or In-Circuit debugger pin. Serial programming clock.

Interrupt on change pin or In-Circuit Debugger pin. Serial programming data.

RC0/T1OSO/

T1CKI

RC1/T1OSI/

CCP2

RC2/CCP1

RC3/SCK/SCL

15

16

17

18

16

18

19

20

32

35

36

37

I/O

I/O

I/O

I/O

ST

ST

ST

ST

PORTC is a bi-directional I/O port.

RC0 can also be the Timer1 oscillator output or a Timer1 clock input.

RC1 can also be the Timer1 oscillator input or Capture2 input/Compare2 output/PWM2 output.

RC2 can also be the Capture1 input/Compare1 output/PWM1 output.

RC3 can also be the synchronous serial clock input/output for both SPI and I2C modes.

22

RC4/SDI/SDA

RC5/SDO

RC6/TX/CK

RC7/RX/DT

23

24

25

26

25

26

27

29

42

43

44

1

I/O

I/O

I/O

I/O

ST

ST

ST

ST

RC4 can also be the SPI Data In (SPI mode) or data I/O (I2C mode).

RC5 can also be the SPI Data Out (SPI mode).

RC6 can also be the USART Asynchronous Transmit or Synchronous Clock.

RC7 can also be the USART Asynchronous Receive or Synchronous Data.

RD0/PSP0

RD1/PSP1

RD2/PSP2

RD3/PSP3

RD4/PSP4

RD5/PSP5

RD6/PSP6

RD7/PSP7

19

20

21

22

27

28

29

30

21

22

23

24

30

31

32

33

38

39

40

41

2

3

4

5

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

PORTD is a bi-

directional I/O port or

parallel slave port when

interfacing to a

microprocessor bus.

23

RE0/RD/AN5

RE1/WR/AN6

RE2/CS/AN7

8

9

10

9

10

11

25

26

27

I/O

I/O

I/O

ST/TTL(3)

ST/TTL(3)

ST/TTL(3)

PORTE is a bi-directional I/O port.

RE0 can also be read control for the parallel slave port, or analog input5.

RE1 can also be write control for the parallel slave port, or analog input6.

RE2 can also be select control for the parallel slave port, or analog input7.

VSS 12,31 13,34 6,29 P - Ground reference for logic and I/O pins

NC - 1,17,28,40

12,13,

33,34

- These pins are not internally connected. These pins should be left unconnected.

3.8 PORTS DESCRIPTION:

Input/Output Ports

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Some pins for these I/O ports are multiplexed with an alternate function for

the peripheral features on the device. In general, when a peripheral is enabled, that

pin may not be used as a general purpose I/O pin.

3.8.1 PORT A and the TRIS A Register:

PORTA is a 6-bit wide bi-directional port. The corresponding data direction

register is TRISA. Setting a TRISA bit (=1) will make the corresponding PORTA

pin an input, i.e., put the corresponding output driver in a Hi-impedance mode.

Clearing a TRISA bit (=0) will make the corresponding PORTA pin an output, i.e.,

put the contents of the output latch on the selected pin.

Reading the PORTA register reads the status of the pins whereas writing to it

will write to the port latch. All write operations are read-modify-write operations.

Therefore a write to a port implies that the port pins are read; this value is modified,

and then written to the port data latch. Pin RA4 is multiplexed with the Timer0

module clock input to become the RA4/T0CKI pin. The RA4/T0CKI pin is a

Schmitt Trigger input and an open drain output. All other RA port pins have TTL

input levels and full CMOS output drivers. Other PORTA pins are multiplexed with

analog inputs and analog VREF input. The operation of each pin is selected by

clearing/setting the control bits in the ADCON1 register (A/D Control Register1).

The TRISA register controls the direction of the RA pins, even when they are being

used as analog inputs. The user must ensure the bits in the TRISA register are

maintained set when using them as analog inputs.

3.8.1 PORT A FUNCTIONS:

Name Bit# Buffer Function

25

RA0/AN0 bit0 TTL Input/output or analog input

RA1/AN1 bit1 TTL Input/output or analog input

RA2/AN2 bit2 TTL Input/output or analog input

RA3/AN3/VREF bit3 TTL Input/output or analog input or VREF

RA4/TOCKI

bit4 ST

Input/output or external clock input for

Timer0. Output is open drain type

RA5/ /AN4 bit5 TTL Input/output or slave select input for

synchronous serial port or analog input

3.8.2 PORT B and the TRIS B Register:

PORTB is an 8-bit wide bi-directional port. The corresponding data direction

register is TRISB. Setting a TRISB bit (=1) will make the corresponding PORTB

pin an input, i.e., put the corresponding output driver in a hi-impedance mode.

Clearing a TRISB bit (=0) will make the corresponding PORTB pin an

output, i.e., put the contents of the output latch on the selected pin. Three pins of

PORTB are multiplexed with the Low Voltage Programming function; RB3/PGM,

RB6/PGC and RB7/PGD. The alternate functions of these pins are described in the

Special Features Section. Each of the PORTB pins has a weak internal pull-up. A

single control bit can turn on all the pull-ups. This is performed by clearing bit

RBPU (OPTION_REG<7>). The weak pull-up is automatically turned off when the

port pin is configured as an output. The pull-ups are disabled on a Power-on Reset.

Four of PORTB’s pins, RB7:RB4, have an interrupt on change feature. Only

pins configured as inputs can cause this interrupt to occur (i.e. any RB7:RB4 pin

configured as an output is excluded from the interrupt on change comparison). The

26

input pins (of RB7:RB4) are compared with the old value latched on the last read of

PORTB. The “mismatch” outputs of RB7:RB4 are ORed together to generate the

RB Port Change Interrupt with flag bit RBIF (INTCON<0>). This interrupt can

wake the device from SLEEP. The user, in the interrupt service routine, can clear

the interrupt in the following manner:

a) Any read or write of PORTB. This will end the mismatch condition.

b) Clear flag bit RBIF. A mismatch condition will continue to set flag bit

RBIF. Reading PORTB will end the mismatch condition, and allow flag bit RBIF to

be cleared. The interrupt on change feature is recommended for wake-up on key

depression operation and operations where PORTB is only used for the interrupt on

change feature. Polling of PORTB is not recommended while using the interrupt on

change feature. This interrupt on mismatch feature, together with software

configurable pull-ups on these four pins, allow easy interface to a keypad and make

it possible for wake-up on key depression.

3.8.2 PORT B FUNCTIONS:

Name Bit# Buffer Function

RB0/INT bit0 TTL/ST(1) Input/output pin or external interrupt input.

Internal software programmable weak pull-

up

RB1 bit1 TTL Input/output pin. Internal software

programmable weak pull-up

RB2 bit2 TTL Input/output pin. Internal software

programmable weak pull-up

RB3/PGM bit3 TTL Input/output pin or programming pin in LVP

27

mode. Internal software programmable weak

pull-up

RB4 bit4 TTL Input/output pin (with interrupt on change).

Internal software programmable weak pull-

up

RB5 bit5 TTL Input/output pin (with interrupt on change).

Internal software programmable weak pull-

up

RB6/PGC bit6 TTL/ST(2) Input/output pin (with interrupt on change)

or In-Circuit Debugger pin. Internal

software programmable weak pull-up. Serial

programming clock.

RB7/PGD bit7 TTL/ST(2) Input/output pin (with interrupt on change) or In-Circuit Debugger pin. Internal software programmable weak pull-up. Serial programming data.

Legend: TTL = TTL input, ST = Schmitt Trigger input

Note 1: This buffer is a Schmitt Trigger input when configured as the external interrupt.

2: This buffer is a Schmitt Trigger input when used in serial programming mode.

3.8.3 PORT C and the TRIS C Register:

PORTC is an 8-bit wide bi-directional port. The corresponding data

direction register is TRISC. Setting a TRISC bit (=1) will make the corresponding

PORTC pin an input, i.e., put the corresponding output driver in a hi-impedance

28

mode. Clearing a TRISC bit (=0) will make the corresponding PORTC pin an

output, i.e., put the contents of the output latch on the selected pin. PORTC is

multiplexed with several peripheral functions (Table-3.5). PORTC pins have

Schmitt Trigger input buffers. When the I2C module is enabled, the PORTC (3:4)

pins can be configured with normal I2C levels or with SMBUS levels by using the

CKE bit (SSPSTAT <6>).

When enabling peripheral functions, care should be taken in defining TRIS bits for

each PORTC pin. Some peripherals override the TRIS bit to make a pin an output,

while other peripherals override the TRIS bit to make a pin an input. Since the TRIS

bit override is in effect while the peripheral is enabled, read-modify write

instructions (BSF, BCF, XORWF) with TRISC as destination should be avoided.

The user should refer to the corresponding peripheral section for the correct TRIS

bit settings.

3.8.3 PORT C FUNCTIONS:

Name Bit# Buffer

Type

Function

RC0/T1OSO/

T1CKI

bit0 ST Input/output port pin or Timer1

oscillator output/Timer1 clock input

RC1/T1OSI/CCP2 bit1 ST Input/output port pin or Timer1

oscillator input or Capture2

input/Compare2 output/PWM2

output

RC2/CCP1 bit2 ST Input/output port pin or Capture1

input/Compare1 output/PWM1

29

output

RC3/SCK/SCL bit3 ST RC3 can also be the synchronous

serial clock for both SPI and I2C

modes

RC4/SDI/SDA bit4 ST RC4 can also be the SPI Data In (SPI

mode) or data I/O (I2C mode).

RC5/SDO bit5 ST Input/output port pin or Synchronous

Serial Port data output

RC6/TX/CK bit6 ST Input/output port pin or USART Asynchronous Transmit or Synchronous Clock

RC7/RX/DT bit7 ST Input/output port pin or USART Asynchronous Receive or Synchronous Data

Legend: ST = Schmitt Trigger input

3.8.4 PORT D and TRIS D Registers:

This section is not applicable to the 28-pin devices. PORTD is an 8-bit port

with Schmitt Trigger input buffers. Each pin is individually configurable as an input

or output. PORTD can be configured as an 8-bit wide microprocessor Port (parallel

slave port) by setting control bit PSPMODE (TRISE<4>). In this mode, the input

buffers are TTL.

3.8.4 PORT D FUNCTIONS:

Name Bit# Buffer Type Function

30

RD0/PSP0 bit0 ST/TTL(1) Input/output port pin or parallel slave port

bit0

RD1/PSP1 bit1 ST/TTL(1) Input/output port pin or parallel slave port

bit1

RD2/PSP2 bit2 ST/TTL(1) Input/output port pin or parallel slave port

bit2

RD3/PSP3 bit3 ST/TTL(1) Input/output port pin or parallel slave port

bit3

RD4/PSP4 bit4 ST/TTL(1) Input/output port pin or parallel slave port

bit4

RD5/PSP5 bit5 ST/TTL(1) Input/output port pin or parallel slave port

bit5

RD6/PSP6 bit6 ST/TTL(1) Input/output port pin or parallel slave port

bit6

RD7/PSP7 bit7 ST/TTL(1) Input/output port pin or parallel slave port

bit7

Legend: ST = Schmitt Trigger input TTL = TTL input

Note 1: Input buffers are Schmitt Triggers when in I/O mode and TTL buffer when in Parallel Slave Port Mode

3.8.5 PORT E and TRIS E Register:

PORTE has three pins RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7,

which are individually configurable as inputs or outputs. These pins have Schmitt

Trigger input buffers. The PORTE pins become control inputs for the

microprocessor port when bit PSPMODE (TRISE<4>) is set. In this mode, the user

31

must make sure that the TRISE<2:0> bits are set (pins are configured as digital

inputs). Ensure ADCON1 is configured for digital I/O. In this mode the input

buffers are TTL.

PORTE pins are multiplexed with analog inputs. When selected as an analog

input, these pins will read as ‘0’s. TRISE controls the direction of the RE pins, even

when they are being used as analog inputs. The user must make sure to keep the

pins configured as inputs when using them as analog inputs.

3.8.5 PORT E FUNCTIONS:

Name Bit# Buffer Type Function

RE0/ /AN5 bit0 ST/TTL(1) Input/output port pin or read control input in parallel slave port mode or analog input:

1=Not a read operation 0=Read operation. Reads PORTD register (if chip selected)

RE1/ /AN6 bit1 ST/TTL(1) Input/output port pin or write control input in parallel slave port mode or analog input:

1=Not a write operation 0=Write operation. Writes PORTD register (if chip selected)

RE2/ /AN7 bit2 ST/TTL(1) Input/output port pin or write control input in parallel slave port mode or analog input:

1=Device is not selected 0=Device is selected

Legend: ST = Schmitt Trigger input TTL = TTL input

32

Note 1: Input buffers are Schmitt Triggers when in I/O mode and TTL buffers when in Parallel Slave Port Mode.

3.9 MEMORY ORGANIZATION:

There are three memory blocks in each of the PIC16F877 MUCs. The

program memory and Data Memory have separate buses so that concurrent access

can occur. There are three memory blocks in each of the PIC16F87X MCUs. The

Program Memory and Data Memory have separate buses so that concurrent access

can occur and is detailed in this section. The EEPROM data memory block is

detailed in Section 4.0. Additional information on device memory may be found in

the PIC micro Mid-Range Reference Manual.

33

Fig 3.3 Memory Organization

3.9.1 Program memory organization:

The PIC16F877 devices have a 13-bit program counter capable of addressing

8K*14 words of FLASH program memory. Accessing a location above the

physically implemented address will cause a wrap around. The RESET vector is at

0000h and the interrupt vector is at 0004h.

3.9.2 DATA memory organization:

34

The data memory is partitioned into multiple banks which contain the

General Purpose Registers and the special functions Registers. Bits RP1

(STATUS<6) and RP0 (STATYUS<5>) are the bank selected bits.

RP1:RP0 Banks

00 0

01 1

10 2

11 3

Each bank extends up to 7Fh (1238 bytes). The lower locations of each bank

are reserved for the Special Function Registers. Above the Special Function

Registers are General Purpose Registers, implemented as static RAM. All

implemented banks contain special function registers. Some frequently used special

function registers from one bank may be mirrored in another bank for code

reduction and quicker access.

CHAPTER 4

SOFTWARE USED

4.1 INTRODUCTION TO EMBEDDED ‘C’:

35

Embedded is the extension of c language. Embedded C is a compiler which

constitutes more build in function. By using c language it is easy to connect the

comport easily. The embedded c compiler has the bias function to connect the

comport. The command from fussing kit sends from the c program according to

user wish.

4.1.1 HI-TEC ‘C’

HI-TEC ‘C’ is a set of software that translates the program written in the C

language in to executable machine code versions are available which compile the

program for the operation under the host operating system.

Some of the Hi-Tec features are

A simple batch file will compile, assemble and link entire program

The compiler perform strong type checking and issues warning about various constructs which may represent programming errors

The generated code is extremely small and fast in execution A full run time library is provided implementing all standard c input/

output and other function

The source code for all run time routine is provided

A power full general purpose macro-assembler is provided

Programs may be generated to execute under the host operating system or customized for installation in ROM.

36

4.2 PIC TOOLS

The tools used in PIC microcontroller is given below

MP LAB

Mp lab provides the following functions

Create and edit source file

Group files in to projects

Debug source code

Debug executable logic using the simulator

Tools in Mp Lab are

Mp Lab development tool

Mp Lab project manager

Mp Lab editor

Mp Lab –SIM simulator

Mp Lab –ICE emulator

4.3 VARIATION CODE USED:

#include <pic.h>

#include <lcd.h>

void adc_init(void);

37

void adc0(void);

void adc1(void);

void hex_dec_cur(unsigned char);

void set_mode();

static bit relay @ ((unsigned ) & PORTE*8+1);

static bit set @((unsigned) &PORTC*8+0);

static bit ent @((unsigned) &PORTC*8+1);

static bit inc @((unsigned) &PORTC*8+2);

static bit dec @((unsigned) &PORTC*8+3);

unsigned char volt,curr,j,curr_high,curr_low,volt_low,volt_high;

unsigned int temp0,temp1;

void main()

{

TRISC=0x0f;

relay=0;

lcd_init();

38

adc_init();

command(0x80);

lcd_condis("Volt & Curr Moni",16);

command(0xc0);

lcd_condis(" V: C: ",16);

del();

EEPROM_READ(12);

curr_high=EEDATA;

EEPROM_READ(13);

curr_low=EEDATA;

EEPROM_READ(14);

volt_high=EEDATA;

EEPROM_READ(15);

volt_low=EEDATA;

while(1)

{

temp0=0;

adc0();

39

command(0xc3);

hex_dec(volt);

temp0=0;

adc1();

command(0xca);

hex_dec_cur(curr);

if(volt>volt_high || volt<volt_low || curr>curr_high ||

curr<curr_low)relay=1;

if(!set) set_mode();

} //While

} //Main

void adc_init()

{

40

ADCON1=0x02; // 8-channel, Left justified, ADC control

TRISA=0xff; // to select the port A as input port

TRISE=0x00;

}

void adc0()

{

for(j=0;j<10;j++)

{

ADCON0=0x00; // Channel select (Cha: 0)

ADON=1; // ADC module ON

delay(255);

ADCON0 =0x05; // selecting a particular channel and making the

go/done bit high

while(ADCON0!=0X01); // Chk whether conversion finished or not

temp1 = ADRESH; // 8 bit value taken into one variable

temp0 = temp0 + temp1;

}

41

volt=temp0/10;

}

void adc1()

{

for(j=0;j<10;j++)

{

ADCON0=0x08; // Channel select (Cha: 0)

ADON=1; // ADC module ON

delay(255);

ADCON0 =0x0d; // selecting a particular channel and making the

go/done bit high

while(ADCON0!=0X09); // Chk whether conversion finished or not

temp1 = ADRESH; // 8 bit value taken into one variable

temp0 = temp0 + temp1;

}

curr=temp0/10;

}

42

void hex_dec_cur(unsigned char val)

{

h=val/100;

hr=val%100;

t=hr/10;

o=hr%10;

lcd_disp(h+0x30);

lcd_disp(t+0x30);

lcd_disp('.');

lcd_disp(o+0x30);

}

void set_mode()

{

command(0x80);

lcd_condis(" Set Mode ",16);

command(0xC0);

43

lcd_condis("Hig Curr : ",16);

j=0;

while(ent)

{

command(0xca);command(0x0f);

if(!inc){j++; if(j>=255)j=0;hex_dec_cur(j);}

else if(!dec){j--;if(j>=255)j=255;hex_dec_cur(j);}

delay(15000);

}

EEPROM_WRITE(12,j);delay(2000);

EEPROM_READ(12);

curr_high=EEDATA;

del();

command(0xC0);

lcd_condis("Low Curr : ",16);

j=0;

while(ent)

{

44

command(0xca);command(0x0f);

if(!inc){j++; if(j>=255)j=0;hex_dec_cur(j);}

else if(!dec){j--;if(j>=255)j=255;hex_dec_cur(j);}

delay(15000);

}

EEPROM_WRITE(13,j);delay(2000);

EEPROM_READ(13);

curr_low=EEDATA;

del();

command(0xC0);

lcd_condis("Hig Volt : ",16);

j=0;

while(ent)

{

command(0xca);command(0x0f);

if(!inc){j++; if(j>=255)j=0;hex_dec(j);}

else if(!dec){j--;if(j>=255)j=255;hex_dec(j);}

delay(15000);

45

}

EEPROM_WRITE(14,j);delay(2000);

EEPROM_READ(14);

volt_high=EEDATA;

del();

command(0xC0);

lcd_condis("Low Volt : ",16);

j=0;

while(ent)

{

command(0xca);command(0x0f);

if(!inc){j++; if(j>=255)j=0;hex_dec(j);}

else if(!dec){j--;if(j>=255)j=255;hex_dec(j);}

delay(15000);

}

EEPROM_WRITE(15,j);delay(2000);

EEPROM_READ(15);

volt_low=EEDATA;

46

del();

command(0x80);

lcd_condis("Volt & Curr Moni",16);

command(0xc0);

lcd_condis(" V: C: ",16);

}

CHAPTER 5

HARDWARE IMPLEMENTED

5.1 POWER SUPPLY AND ITS BLOCK DIAGRAM:

The ac voltage, typically 220V rms, is connected to a transformer, which

steps that ac voltage down to the level of the desired dc output. A diode rectifier

47

then provides a full-wave rectified voltage that is initially filtered by a simple

capacitor filter to produce a dc voltage. This resulting dc voltage usually has

some ripple or ac voltage variation.

A regulator circuit removes the ripples and also remains the same dc value

even if the input dc voltage varies, or the load connected to the output dc

voltage changes. This voltage regulation is usually obtained using one of the

popular voltage regulator IC units.

Fig 5.1 Power supply block

5.2 WORKING PRINCIPLE OF THE BLOCK:

Transformer:

The potential transformer will step down the power supply voltage (0-230V)

to (0-6V) level. Then the secondary of the potential transformer will be connected

to the precision rectifier, which is constructed with the help of op–amp. The

advantages of using precision rectifier are it will give peak voltage output as DC,

rest of the circuits will give only RMS output.

48

Bridge rectifier:

When four diodes are connected as shown in figure, the circuit is called as

bridge rectifier. The input to the circuit is applied to the diagonally opposite corners

of the network, and the output is taken from the remaining two corners.Let us

assume that the transformer is working properly and there is a positive potential, at

point A and a negative potential at point B. the positive potential at point A will

forward bias D3 and reverse bias D4.

The negative potential at point B will forward bias D1 and reverse D2. At

this time D3 and D1 are forward biased and will allow current flow to pass through

them; D4 and D2 are reverse biased and will block current flow. The path for

current flow is from point B through D1, up through RL, through D3, through the

secondary of the transformer back to point B. this path is indicated by the solid

arrows. Waveforms (1) and (2) can be observed across D1 and D3.

One-half cycle later the polarity across the secondary of the transformer

reverse, forward biasing D2 and D4 and reverse biasing D1 and D3. Current flow

will now be from point A through D4, up through RL, through D2, through the

secondary of T1, and back to point A. This path is indicated by the broken arrows.

Waveforms (3) and (4) can be observed across D2 and D4. The current flow

through RL is always in the same direction. In flowing through RL this current

develops a voltage corresponding to that shown waveform (5). Since current flows

through the load (RL) during both half cycles of the applied voltage, this bridge

rectifier is a full-wave rectifier.

49

One advantage of a bridge rectifier over a conventional full-wave rectifier is

that with a given transformer the bridge rectifier produces a voltage output that is

nearly twice that of the conventional full-wave circuit. This may be shown by

assigning values to some of the components shown in views A and B. assume that

the same transformer is used in both circuits. The peak voltage developed between

points X and y is 1000 volts in both circuits. In the conventional full-wave circuit

shown—in view A, the peak voltage from the center tap to either X or Y is 500

volts. Since only one diode can conduct at any instant, the maximum voltage that

can be rectified at any instant is 500 volts. The maximum voltage that appears

across the load resistor is nearly-but never exceeds-500 v0lts, as result of the small

voltage drop across the diode. In the bridge rectifier shown in view B, the maximum

voltage that can be rectified is the full secondary voltage, which is 1000 volts.

Therefore, the peak output voltage across the load resistor is nearly 1000 volts.

With both circuits using the same transformer, the bridge rectifier circuit produces a

higher output voltage than the conventional full-wave rectifier circuit.

IC voltage regulators:

Voltage regulators comprise a class of widely used Ics. Regulator IC units

contain the circuitry for reference source, comparator amplifier, control device, and

overload protection all in a single IC. IC units provide regulation of either a fixed

positive voltage, a fixed negative voltage, or an adjustably set voltage. The

regulators can be selected for operation with load currents from hundreds of milli

amperes to tens of amperes, corresponding to power ratings from milli watts to tens

of watts.

50

Fig. 5.2 Voltage Regulator for 5 V

Fig. 5.3 Voltage Regulator for 12 V

A fixed three-terminal voltage regulator has an unregulated dc input voltage,

Vi, applied to one input terminal, a regulated dc output voltage, Vo, from a second

terminal, with the third terminal connected to ground.

The series 78 regulators provide fixed positive regulated voltages from 5 to

24 volts. Similarly, the series 79 regulators provide fixed negative regulated

voltages from 5 to 24 volts.

For ICs, microcontroller, LCD --------- 5 volts

51

For alarm circuit, op-amp, relay circuits ---------- 12 volts

5.3 VOLTAGE MEASUREMENT:

This circuit is designed to monitor the supply voltage. The supply voltage

that has to monitor is step down by the potential transformer. Usually we are using

the 0-6v potential transformer. The step down voltage is rectified by the precision

rectifier. The precision rectifier is a configuration obtained with an operational

amplifier in order to have a circuit behaving like an ideal diode or rectifier.

The full wave rectifier is the combination of half wave precision rectifer and

summing amplifier. When the input voltage is negative, there is a negative voltage

on the diode, too, so it works like an open circuit, there is no current in the load and

the output voltage is zero. When the input is positive, it is amplified by the

operational amplifier and it turns the diode on. There is current in the load and,

because of the feedback, the output voltage is equal to the input.

In this case, when the input is greater than zero, D2 is ON and D1 is OFF, so

the output is zero. When the input is less than zero, D2 is OFF and D1 is ON, and

the output is like the input with an amplification of − R2 / R1. The full-wave rectifier

depends on the fact that both the half-wave rectifier and the summing amplifier are

precision circuits. It operates by producing an inverted half-wave-rectified signal

and then adding that signal at double amplitude to the original signal in the

summing amplifier. The result is a reversal of the selected polarity of the input

signal. Then the output of the rectified voltage is adjusted to 0-5v with the help of

variable resistor VR1. Then given to ripples are filtered by the C1 capacitor. After

the filtration the corresponding DC voltage is given to ADC or other related circuit.

52

Fig. 5.4 Voltage Measurement Circuit

5.4 CURRENT MEASUREMENT:

This circuit is designed to monitor the supply current. The supply

current that has to monitor is step down by the current transformer. The step down

current is converted by the voltage with the help of shunt resistor. Then the

converted voltage is rectified by the precision rectifier. The precision rectifier is a

configuration obtained with an operational amplifier in order to have a circuit

behaving like an ideal diode or rectifier.

53

The full wave rectifier is the combination of half wave precision rectifer and

summing amplifier. When the input voltage is negative, there is a negative voltage

on the diode, too, so it works like an open circuit, there is no current in the load and

the output voltage is zero. When the input is positive, it is amplified by the

operational amplifier and it turns the diode on. There is current in the load and,

because of the feedback, the output voltage is equal to the input.

In this case, when the input is greater than zero, D2 is ON and D1 is OFF, so

the output is zero. When the input is less than zero, D2 is OFF and D1 is ON, and

the output is like the input with an amplification of − R2 / R1. The full-wave rectifier

depends on the fact that both the half-wave rectifier and the summing amplifier are

precision circuits. It operates by producing an inverted half-wave-rectified signal

and then adding that signal at double amplitude to the original signal in the

summing amplifier. The result is a reversal of the selected polarity of the input

signal. Then the output of the rectified voltage is adjusted to 0-5v with the help of

variable resistor VR1. Then given to ripples are filtered by the C1 capacitor. After

the filtration the corresponding DC voltage is given to ADC or other related circuit.

54

Fig. 5.5 Current Measurement Circuit

5.5 RELAY

A relay is an electrically operated switch. Current flowing through the coil of

the relay creates a magnetic field which attracts a lever and changes the switch

contacts. The coil current can be on or off so relays have two switch positions and

they are double throw (changeover) switches. Relays allow one circuit to switch a

second circuit which can be completely separate from the first. For example a low

voltage battery circuit can use a relay to switch a 230V AC mains circuit.

55

There is no electrical connection inside the relay between the two circuits;

the link is magnetic and mechanical. The coil of a relay passes a relatively large

current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays

designed to operate from lower voltages. Most ICs (chips) cannot provide this

current and a transistor is usually used to amplify the small IC current to the larger

value required for the relay coil. The maximum output current for the popular 555

timer IC is 200mA so these devices can supply relay coils directly without

amplification.

Fig Relay types

Relays are usually SPDT or DPDT but they can have many more sets of

switch contacts, for example relays with 4 sets of changeover contacts are readily

available. Most relays are designed for PCB mounting but you can solder wires

directly to the pins providing you take care to avoid melting the plastic case of the

relay. The animated picture shows a working relay with its coil and switch

contacts. You can see a lever on the left being attracted by magnetism when the coil

is switched on. This lever moves the switch contacts. There is one set of contacts

(SPDT) in the foreground and another behind them, making the relay DPDT.

56

Fig Relay internal connection

The relay's switch connections are usually labeled COM, NC and NO:

COM = Common, always connect to this. It is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

5.5.1 Circuit Description:

This circuit is designed to control the load. The load may be motor or any

other load. The load is turned ON and OFF through relay. The relay ON and OFF

is controlled by the pair of switching transistors (BC 547). The relay is connected in

the Q2 transistor collector terminal. A Relay is nothing but electromagnetic

switching device which consists of three pins. They are Common, Normally close

(NC) and Normally open (NO).

The relay common pin is connected to supply voltage. The normally open

(NO) pin connected to load. When high pulse signal is given to base of the Q1

transistors, the transistor is conducting and shorts the collector and emitter terminal

and zero signals are given to base of the Q2 transistor. So the relay is turned OFF

state.

57

When low pulse is given to base of transistor Q1 transistor, the transistor is

turned OFF. Now 12v is given to base of Q2 transistor so the transistor is

conducting and relay is turned ON. Hence the common terminal and NO terminal of

relay are shorted. Now load gets the supply voltage through relay.

Voltage Signal from Microcontroller or PC

Transistor

Q1

Transistor

Q2

Relay

1 ON OFF OFF

0 OFF ON ON

Fig. 5.6 Relay Circuit

58

5.5.2 Choice of Relay:

You need to consider several features when choosing a relay:

1. Physical size and pin arrangement:

If you are choosing a relay for an existing PCB you will need to ensure that

its dimensions and pin arrangement are suitable. You should find this

information in the supplier's catalogue.

2. Coil voltage:

The relay's coil voltage rating and resistance must suit the circuit powering

the relay coil. Many relays have a coil rated for a 12V supply but 5V and

24V relays are also readily available. Some relays operate perfectly well with

a supply voltage which is a little lower than their rated value.

3. Coil resistance:

The circuit must be able to supply the current required by the relay coil. You

can use Ohm's law to calculate the current:

Relay coil current = Supply voltage/Coil resistance

For example: A 12V supply relay with a coil resistance of 400 passes a

current of 30mA. This is OK for a 555 timer IC (maximum output current

200mA), but it is too much for most ICs and they will require a transistor to

amplify the current.

4. Switch ratings (voltage and current):

The relay's switch contacts must be suitable for the circuit they are to control.

You will need to check the voltage and current ratings. Note that the voltage

rating is usually higher for AC, for example: "5A at 24V DC or 125V AC".

59

5. Switch contact arrangement (SPDT, DPDT):

Most relays are SPDT or DPDT which are often described as "single pole

changeover" (SPCO) or "double pole changeover" (DPCO). For further

information please see the page on switches.

PROTECTION DIODES FOR RELAY:

Transistors and ICs (chips) must be protected from the brief high voltage

'spike' produced when the relay coil is switched off. The diagram shows how a

signal diode (e.g. IN4148) is connected across the relay coil to provide this

protection. Note that the diode is connected 'backwards' so that it will normally not

conduct. Conduction only occurs when the relay coil is switched off, at this moment

current tries to continue flowing through the coil and it is harmlessly diverted

through the diode. Without the diode no current could flow and the coil would

produce a damaging high voltage 'spike' in its attempt to keep the current flowing.

Advantages of relays:

Relays can switch AC and DC, transistors can only switch DC. Relays can

switch high voltages, transistors cannot.

Relays are a better choice for switching large currents (> 5A).

Relays can switch many contacts at once.

Disadvantages of relays:

Relays are bulkier than transistors for switching small currents.

60

Relays cannot switch rapidly (except reed relays), transistors can switch

many times per second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many chips can provide, so a low power

transistor may be needed to switch the current for the relay's coil.

5.6 LCD DISPLAY:

Liquid crystal displays (LCDs) have materials which combine the properties

of both liquids and crystals. Rather than having a melting point, they have a

temperature range within which the molecules are almost as mobile as they would

be in a liquid, but are grouped together in an ordered form similar to a crystal. An

LCD consists of two glass panels, with the liquid crystal material sand witched in

between them. The inner surface of the glass plates are coated with transparent

electrodes which define the character, symbols or patterns to be displayed

polymeric layers are present in between the electrodes and the liquid crystal, which

makes the liquid crystal molecules to maintain a defined orientation angle.

One each polarizer’s are pasted outside the two glass panels. This

polarizer’s would rotate the light rays passing through them to a definite angle, in a

particular direction. When the LCD is in the off state, light rays are rotated by the

two polarizers and the liquid crystal, such that the light rays come out of the LCD

without any orientation, and hence the LCD appears transparent.

61

When sufficient voltage is applied to the electrodes, the liquid crystal

molecules would be aligned in a specific direction. The light rays passing through

the LCD would be rotated by the polarizer’s, which would result in activating /

highlighting the desired characters. The LCD’s are lightweight with only a few

millimeters thickness. Since the LCD’s consume less power, they are compatible

with low power electronic circuits, and can be powered for long durations. The

LCD does don’t generate light and so light is needed to read the display. By using

backlighting, reading is possible in the dark. The LCD’s have long life and a wide

operating temperature range. Changing the display size or the layout size is

relatively simple which makes the LCD’s more customer friendly.

The LCDs used exclusively in watches, calculators and measuring

instruments are the simple seven-segment displays, having a limited amount of

numeric data. The recent advances in technology have resulted in better legibility,

more information displaying capability and a wider temperature range. These have

resulted in the LCDs being extensively used in telecommunications and

entertainment electronics. The LCDs have even started replacing the cathode ray

tubes (CRTs) used for the display of text and graphics, and also in small TV

applications. Crystalonics dot–matrix (alphanumeric) liquid crystal displays are

available in TN, STN types, with or without backlight. The use of C-MOS LCD

controller and driver ICs result in low power consumption. These modules can be

interfaced with a 4-bit or 8-bit microprocessor /Micro controller.

5.6.1 Features of LCD

The built-in controller IC has the following features:

Correspond to high speed MPU interface (2MHz)

62

80 x 8 bit display RAM (80 Characters max)

9,920-bit character generator ROM for a total of 240 character fonts. 208

character fonts (5 x 8 dots) 32 character fonts (5 x 10 dots)

64 x 8 bit character generator RAM 8 character generator RAM 8 character

fonts (5 x 8 dots) 4 characters fonts (5 x 10 dots)

Programmable duty cycles

1/8 – for one line of 5 x 8 dots with cursor

1/11 – for one line of 5 x 10 dots with cursor

1/16 – for one line of 5 x 8 dots with cursor

Wide range of instruction functions display clear, cursor home, display on/off,

cursor on/off, display character blink, cursor shift, display shift.

Automatic reset circuit, which initializes the controller / driver ICs after

power on.

5.6.2 Applications:

Personal computers, word processors, facsimiles, telephones, etc.

5.7 KEYPAD

Keypad is used to enter the predefined values of the power transformer.

Keypad with four keys is employed. The operations of the keys are to increment

and decrement the values to be set.

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CHAPTER 6

CONCLUSION

Transformers are static devices, totally enclosed and generally oil immersed.

Therefore chances of faults occurring on them are very rare. However the

consequences of even a rare fault may be very serious unless the transformer is

quickly disconnected from the system. This necessitates to provide adequate

automatic protection for transformers against possible faults. The major faults on

transformers occur due to short circuits in the transformers or in their connections.

The basic system used for protection against these faults is the differential relay

scheme.

Protection of power transformer is a big challenge nowadays. By the help of

microcontroller-based relay, protection of transformer is performed very quickly

and accurately. This system provides a better and safer protection than the other

methods which are currently in use. The advantages of this system over the current

methods in use are fast response, better isolation and accurate detection of the fault.

This system overcomes the other drawbacks in the existing systems such as

maintenance and response time.

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REFERENCES

1. Guzman, A., S. Zocholl and G.Benmouyal, 2000. “Performance analysis of

traditional and improved transformer differential protective relays. Hector J.

Altue (Universidad Autonoma de Nuevo Leon) SEL.

2. Guzman, A., S. Zocholl, G.Benmouyal, and H.J.Altuve 2001. “A current

based solution for differential protection IEEE Trans., Power Deliv.,

3. Mao, P.L. and R.K. Aggarwal, 2001. A novel approach to the classification

of transient phenomena in power transformers using combined wavelet

transform and neural network. IEEE Trans. Power Deliv., 16:4

4. Sidhu, T.S., M.S. Sachdev and M. Hfuda, 1996 Computer simulation of

protective relay design for evaluation their performance. Power System

Research Group University of Saskatchewan, Canada.

5. Sachdev M.S., T.S. Sidhu and H.C. Wood, 1989. A digital relaying

algorithm for detecting transformer winding faults. IEEE Trans. Power

Deliv., 43:1638-1648.

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